The present invention relates to the field of communication technology, and more specifically, to a method and apparatus for signal modulation.
In the prior art, some frequency bands are licensed to some communities or entities by particular authorities. These bands are called as licensed bands, which refer to those bands that can be used under licenses. Authorities that are responsible for issuing band licenses may comprise, for example, government departments or communication organizations and so on.
Generally, in Frequency Division Multiple Access (FDMA) based wireless communication systems (for example, the Personal Phone System (PHS) or OFDM systems such as Wimax, LET systems and so on), the licensed band may be divided into multiple sub-bands having the same bandwidth. Those multiple sub-bands may be utilized by several communication entities. Communication entities determine available sub-bands through scanning. The available sub-bands may be discrete, i.e., at least one unavailable sub-band may be found between multiple available sub-bands and separate said multiple available sub-bands from each other. A communication entity may be, for example, a base station, a mobile terminal, or a set of synchronized base stations and the like. Such communication entities are out of synchronization, or use different communication techniques.
In a system with discrete sub-bands in the prior art, each entity utilize a sub-band. A guard band is provided between two continuous sub-bands to prevent interference therebetween. In the prior art, each sub-band comprises two parts, i.e., an effective band and a guard band, wherein only the effective band may be used for signal transmission.
In a scheme in the prior art, several sub-bands are collected together and their effective bands are used for signal modulation.